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With all of today’s focus on new technologies and processes, we often forget how we got here. This may be especially true in the push for a true digital denture—one that can be fabricated with CAD/CAM technology, needing fewer patient visits and resulting in faster turnaround time and more accurate fit. As with all of today’s technology, the ability to fabricate any prosthesis hinges on understanding the history of each. Knowing why we use the analog process at certain points is also key to being able to fabricate the same prosthesis utilizing digital technology.
Implant restorations for edentulous patients have been established as a predictable, successful treatment modality for many years. On some occasions, however, implants may not always be indicated for financial or other reasons. With better hygiene today, patients are maintaining their natural teeth longer than ever, leading some to speculate if dentures will continue to be necessary in the near future. Edentulism has declined by 10% every decade for the last 30 years. However, it is also estimated that the adult population will increase by 79% between 1991 and 2020 offsetting this decline in edentulism.1 As a result, it is safe to say there will be a growing base of patients requiring dentures, which will increase the demand for technology in this sector in order to provide better restorations for patients.
Critical Fabrication Steps
Digital dentures provide an attractive alternative to the traditional denture fabrication process. In order to understand the digital denture process, one must understand the steps needed to fabricate a typical traditional denture. Traditionally, preliminary impressions are made with alginate and then sent to the lab to fabricate a custom tray. The custom tray is taken to the mouth, usually using border molding with compound, and the critical anatomical structures are captured in a final impression (Figure 1). The laboratory then takes this information and fabricates the master cast, record base, and wax rims (Figure 2), which are returned to the dentist’s office for the patient to try in.2,3
This appointment is one of the key steps in the fabrication of a traditional denture. The record base is utilized to ensure the extension and vestibular areas are adequate and fit correctly for patient comfort and function. The wax rims are contoured for lip support, future incisal edge position, occlusal position, and vertical dimension. The midline can also be marked on the wax (Figure 3). A facebow or bite fork can be utilized to further refine the correct vertical dimension. In addition, the patient and dentist choose the shade and mold that they prefer for the case. This appointment tends to be the longest since it establishes the foundation that all future work is built upon.2,3
For the next appointment, the dentist receives a denture set-up to try in. Here is the final chance to make any substantial changes to the denture. The dentist verifies the fit, esthetics, vertical dimension, and phonetics (Figure 4 and Figure 5) to ensure that the patient can speak, verify the tooth shape, and select the shade. Because the set-up is normally in wax, there is wide latitude to make changes in position, fit, and feel for the patient. Once both patient and dentist are satisfied, the set-up is returned to the laboratory for final processing. On the laboratory side, after processing, the dentures should be checked again to ensure no changes happened during the process and are returned to the dentist ready for insertion.3,4
Traditional denture development takes at least five visits, with more possible if there are errors or changes needed at any stage. This is a tried-and-true process that hasn’t drastically changed over the last 30 years. With today’s focus on emerging technology and materials, many companies are trying to leverage new manufacturing processes to reduce patient visits, make the process simpler, and still return a proper restoration. The first step is capturing the data. There are numerous intraoral impression scanners on the market today, but using them to scan the edentulous arch is still very difficult. There is no precise way to capture the vestibular area nor pick up the edentulous arch accurately.5 Therefore, all of today’s digital dentures still require traditional impressions.
Digital Workflow
There are multiple companies delivering digital dentures, but for this article the author focuses on the most popular providers: AvaDent™ Digital Denture Solutions and Pala™ Digital Dentures. There are other companies that follow roughly the same workflow. To achieve better efficiency and results, these companies look to combine steps to reduce chairtime and increase accuracy. Since intraoral impression scanners are still not ready to scan edentulous cases, the first step will inevitably be acquiring records utilizing a combination of traditional methods and new workflows.
A transitional system that was introduced prior to a completely digital denture workflow is the Good Fit™ impression system, which utilizes moldable PMMA trays that can be custom fit to a patient’s mouth (Figure 6). This allows the dentist to construct a type of custom tray that ensures proper borders and soft tissue impressions. The trays can be adjusted to allow the proper vertical dimension and occlusion plane as well as establish centric relation. This system is intended to combine all the initial steps of a traditional denture workflow. The results are sent to the laboratory for denture set-up and all the remaining steps.6
There are notable benefits to this system. It allows the dentist to consolidate the steps required to fabricate the denture. In addition, the patient gets to see what the final case will look like and to check phonetics and shade. The dentist has full control, able to add or remove from the trays, as well as mark the midline and incisal positions. The concept is that the dentist combines all those steps of the traditional protocol to ensure the final case fits better and avoids the issue of multiple set-ups or adjustments. This protocol still uses the traditional fabrication process after the initial impression, and a denture set-up will be tried in before processing. An important note is that if there was any error during the initial appointment, it can be corrected during the set-up try-in stage.
Digital dentures build upon this principle. They, too, combine the initial appointments into one visit. They utilize various methods including the Good Fit protocol to establish the initial records. The difference is instead of going to a traditional fabrication process, the dentures are now milled or printed. In the past, this meant there was no try-in appointment. Today, the systems have incorporated try-in stages to help offset some of the problems of going straight to finish. If there was a mistake or if any step was overlooked during the records stage, there is now a chance to correct the problems before going to finish.
All digital denture systems have a proprietary system for capturing all the key record information in one visit. Reverting back to the traditional record-taking denture protocol, the new digital workflow by the time of the denture set-up results in establishing: accurate models of the patient’s soft tissue, occlusal plane, vertical dimension and centric, midline and incisal tooth positions, proper lip support and choice of a mold and tooth shade. AvaDent and Pala each have their own methods for acquiring this data (Figure 7 through Figure 9).7,8 The key to a successful digital denture is accurately acquiring all the required records.
This also brings us full circle to any traditional workflow. The key to success is accurate record taking at each step. The reason the process is broken down into steps here is both to verify the previous step as well as to bring attention to the possibility for human error in manufacturing. As long as the proper records are taken, digital dentures allow us to remove some of that human error in the fabrication process. Digital dentures increase the predictability of the treatment outcome and reduce the number of appointments.9 Again, success hinges on a dentist being even more vigilant in the first record-taking step, as any error will require additional work.
The biggest change is on the manufacturing side of digital dentures. No longer are there wax set-ups, flasking, or acrylic processing. All the steps have been transferred to CAD/CAM fabrication technology (Figure 10 and Figure 11). All the digitally captured record data is input into CAD/CAM software digital tooth set-up and design of the denture base. There is no chance for distortion or loss of information between steps because everything is completed virtually. Dentists and patients can view the denture digitally before fabrication, and if there is any question a special try-in version can be created to ensure that everything is verified before the final prosthesis is fabricated.
Today’s milled and printed dentures have clear advantages over their handmade counterparts. Key benefits of digital dentures include, “significantly reduced dentist time, and improved retention and digital archiving.”10 Fewer patient visits result in less chairtime, and improved retention can be attributed to the manufacturing process. As shown by other CAD/CAM manufacturing processes, virtually designed and milled or printed dentures have a better fit by reducing the human error associated with the traditional process (Figure 12 through Figure 14). Finally, digital archiving is highly beneficial for both the patient and dentist. No longer does one need to keep stone models, and if a patient relocates to another city or state, their records can be easily transferred.
A proper, well-fitting denture is one of the most difficult restorations to make. Today’s digital technology has helped reduce the number of steps required to make the restoration, and the manufacturing processes have removed some of the human error. But with the enhanced manufacturing and reduced chairtime comes an even more important need for all the steps to be completed accurately. All the records need to be accurate, and there are no shortcuts. Digitization has taken a very difficult process and consolidated the steps, which means that each step needs even more attention than before.
Basic Principles, Not Ancient History
History plays a key role in all of today’s technology. The need for complete dentures is not going away; in fact it is slated to grow over the next few years. Without understanding why it’s necessary to take certain records, it’s possible to skip or gloss over an important detail that is the foundation for the restoration. Know too that not every patient may be suitable for the digital process, and it’s been shown that patient selection may have an effect on the positivity of some of the outcomes.10 Therefore, just like not every edentulous patient is best served by a fixed case, not every denture case should be produced digitally.
Digital dentures is an exciting new field in the evolution of CAD/CAM dentistry. When each step is completed properly, the result is a better fitting restoration, less time wasted, higher patient satisfaction, and significantly reduced chairtime. However, if any step of the record-taking phase is missed or done incorrectly, it can compound the problems and require either a complete redo or additional steps to fix the problem.
Therefore, it’s critical to identify the right candidates for digital dentures. There is no question that digital denture process will grow as a share of the market, and newer systems may emerge to help lessen the chance for error in the initial record taking stage. But the need for traditionally made dentures will never go away. In fact, understanding conventional denture protocol may become even more important in cases where the digital denture needs adjustment if fit is not quite right when fabricated.
As with any new technology, digital denture fabrication is built on a foundation that many may soon forget, and it’s imperative that both the dentist and laboratory remember the value and purpose of each step of the traditional process before reducing those steps. Otherwise we are liable to deliver a sub-par product to our patients in the name of innovation.
References
1. Douglass CW, Shih A, Ostry L. "Will there be a need for complete dentures in the United States in 2020?" The Journal of Prosthetic Dentistry. 2002;87.1:5-8.
2. Zarb GA, Hobkirk JA, Eckert SE, et al. Prosthodontic treatment for edentulous patients: Complete dentures and implant-supported prostheses. 13th ed. St. Louis, MO: Mosby; 2013.
3. Zitzmann NU, Marinello CP. Treatment plan for restoring the edentulous maxilla with implant-supported restorations: Removable overdenture versus fixed partial design. The Journal of Prosthetic Dentistry. 1999;82:188-96.
4. Sadowsky SJ. The role of complete denture principles in implant prosthodontics. Journal of the California Dental Association. 2003;13:905-909.
5. Andriessen FS, Rijkens DR, Van Der Meer WJ, Wismeijer DW. "Applicability and accuracy of an intraoral scanner for scanning multiple implants in edentulous mandibles: A pilot study." The Journal of Prosthetic Dentistry. 2014;111.3:186-94.
6. Good Fit. Denture Tray. Available at: https://goodfit.com. Accessed January 15, 2017.
7. AvaDent Digital Dentures. Record Methods. Available at: www.avadent.com. Accessed January 15, 2017.
8. Pala Digital Dentures. Patient Videos. Available at: www.paladigitaldentures.com. Accessed January 15, 2017.
9. Schweiger J, Güth J-F, Edelhoff D, Stumbaum J. Virtual evaluation for CAD-CAM-fabricated complete dentures. The Journal of Prosthetic Dentistry. 2017;117.1: 28-33.
10. Kattadiyil MT, Alhelal A. An update on computer-engineered complete dentures: A systematic review on clinical outcomes. The Journal of Prosthetic Dentistry. 2017;117(4):478-485.
About the Author
Justin Hayes
Marotta Dental Studio, Inc.
Farmingdale, NY
Disclosure: The author had no disclosures to report.
